With advances in technology, there is a continuous demand to increase data transmission rates and volume of data transmission. Traditional communication lines, such as cable containing copper wire, have been used to cater to this continuously growing demand, however, traditional communication lines are subject to many disadvantages. Traditional communication lines are susceptible to interference during the transmission of data. Examples of such interference include, but are not limited to, electromagnetic interference and inter-symbol interference. Traditional communication lines are also characterized by a limited bandwidth, thereby limiting the amount of data that may be transmitted via traditional communication lines.
Fiber-optic telecommunication systems have been introduced to the telecommunication industry to overcome the shortcomings of traditional communication lines. Fiber-optic telecommunication systems are characterized by immunity to electromagnetic interference. Specifically, fiber-optic telecommunication uses optical fiber for the transmission of information. Since optical fiber transmits light, rather than electrons, optical fiber does not radiate electromagnetic fields. In addition, fiber-optic telecommunication systems have high bandwidths for the transmission of information. As is known by those of ordinary skill in the art, high bandwidth permits longer transmission distances and higher signal transmission rates.
A basic fiber-optic network contains a transmitter, a fiber-optic cable, and a receiver. The transmitter contains a light-emitting diode (LED), laser diode (LD), an edge-emitting laser, a vertical cavity surface-emitting laser (VCSEL), or any other device that converts an electrical signal into an optical signal for transmission via the fiber-optic cable. The receiver typically contains a photodiode that converts the transmitted light back into an electrical signal, and an amplifier for enabling easier detection of the electrical signal via amplification of the electrical signal.
It is generally desirable for lasers that are used in fiber optic telecommunication systems to produce light at a single, relatively long wavelength, in the range from approximately 1.2-1.6 micrometers (μm). Light in the wavelength range from approximately 1.2-1.6 μm can be transmitted by an optical fiber with relatively little loss of signal intensity, attenuation, or absorption over long distances. However, emission in the range of 1.2-1.6 μm requires the semiconductor laser to be fabricated from materials having a corresponding bandgap energy. Photons in semiconductors are further discussed in B. Saleh et al., Fundamentals of Photonics, pp. 543-643 (1991), which is incorporated herein by reference.
Currently, a semiconductor laser operating in the 1.3 μm wavelength region is grown using indium gallium arsenide phosphide (InGaAsP) in its active region on an InP wafer. However, it is difficult to grow high quality distributed Bragg reflectors (DBRs) of a vertical cavity surface-emitting laser (VCSEL) using InGaAsP material. Therefore, InGaAsP lasers typically have DBRs of materials other than InGaAsP.
Indium gallium arsenide nitride (InGaAsN) is an attractive material for the active region of long wavelength edge-emitting lasers and VCSELs since high-quality InGaAsN can be grown on a gallium arsenide (GaAs) wafer. The juxtaposition InGaAsN and GaAs results in a high conduction band offset. Moreover, such devices can use highly-reflective GaAs/aluminum arsenide (AlAs) DBRs. However, using InGaAsN in a semiconductor gives rise to significant manufacturing challenges.
InGaAsN edge-emitting lasers and VCSELs capable of continuous wave operation are typically grown by metalorganic chemical vapor deposition (MOCVD), which is generally suitable for mass production. Dimethylhydrazine (DMHy) has been used as a nitrogen precursor in InGaAsN MOCVD growth. This nitrogen precursor, DMHy, has a few advantages. DMHy has a low decomposition temperature and therefore is suitable for InGaAsN MOCVD growth where the growth temperature is typically low (500-600 degrees Celsius). In addition, DMHy is a liquid and has reasonably high vapor pressure at room temperature.
There are, however, negative aspects associated with the use of DMHy as a nitrogen precursor. In order to obtain a laser capable of emission in the 1.3 μm range, for instance, InGaAsN having a mole fraction of In0.38Ga0.62As0.99N0.01 is required. However, due to extremely low N incorporation in InGaAsN by MOCVD with DMHy as the N precursor, a ratio of more than 95% DMHy/total group-V precursor ratio is supplied to an MOCVD reactor to obtain 1% N/total group-V atoms in solid composition, resulting in large consumption of DMHy. In addition, the following InGaAsN quality issues result from use of DMHy as a nitrogen precursor.
In order to enhance N incorporation in InGaAsN and to achieve a very high DMHy/total group-V precursor ratio (e.g., more than 95%), a very low As/group III ratio (e.g., approximately 5%) is required. Unfortunately, a low As/group III ratio typically causes poor material quality in GaAs based semiconductors. In accordance with the example characterized by a very high DMHy/total group-V precursor ratio and a very low As/group III ratio, the ratio of precursor for group III, As, and N is 1:5:100. In addition, the sticking coefficient of N for the example is estimated to be approximately 0.0001.
Another negative aspect associated with the use of DMHy as a nitrogen precursor is that the purity of DMHy is currently difficult to control, especially for residual water level. Water contamination in DMHy causes poor material quality of semiconductors. As mentioned above, a laser operating with a wavelength of approximately 1.3 μm requires a large DMHy/total group-V precursor ratio for InGaAsN growth. The required large ratio results in a large amount of DMHy being supplied to the MOCVD reactor, resulting in opportunities for the incorporation of impurities, such as, but not limited to, oxygen, into the InGaAsN.
In addition, the incorporation of N is proportional to the mole fraction composition of In in InGaAsN. Higher In fractions tend to dramatically reduce N incorporation in InGaAsN. Therefore, it is difficult to obtain 1.55 μm emission from InGaAsN, which should have 40% In and 3% N, by MOCVD growth and with using DMHy as a N precursor.
Therefore, it is desirable to find more suitable nitrogen precursors for growth of high quality InGaAsN for semiconductor lasers such as, but not limited to, edge-emitting lasers and surface-emitting lasers.